Mobile communication systems, such as the universal mobile telecommunications system (UMTS) can carry both voice and data traffic via fixed, wireless and satellite networks. These communication systems are incessantly evolving, thereby also developing and providing packet frameworks for the delivery of IP based, real-time, conversational or multimedia services. For instance, an IP multimedia subsystem (IMS) standard is specified by the 3rd Generation Partnership Project (3GPP) (see 3GPP TS 23.228 v6.9.0: “IP Multimedia Subsystem (IMS); Stage 2 (Release 6)”, incorporated herein by reference, available from http://www.3gpp.org). IMS is specifically architected to enable and enhance real time, mobile and fixed multimedia mobile services such as rich voices services, video telephony, messaging, conferencing and push services. IMS runs over the standard Internet Protocol (IP) and supports both packet-switched and circuit-switched phone systems.
Typically, multiple users are subscribed to receive IMS services, such as Push to Talk over Cellular (PoC) or Video-conferencing services, which occasionally includes providing the same data to multiple users in a specific cell of a radio network. IMS standards however only support point-to-point (PTP) connections to the mobile terminals (MT) of the users, including the reservation of system resources in the radio access network (RAN) for dedicated radio bearer connectivity to each mobile terminal provided with the service.
In cases where multiple users receive the same service, it can be advantageous to use a multicast capable service with a point-to-multipoint (PTM) capability to transmit the service data to the multiple users. When providing IMS services in an UMTS system, typically, shared or broadcast radio bearers instead of many dedicated radio bearers are utilized to serve multiple users in a radio cell, which may save system resources in the radio access network.
A multicast capable service is for example the Multimedia Broadcast/Multicast Service (MBMS), which has also been standardized by the 3GPP (see 3GPP TS 23.246 v6.6.0: “Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description (Release 6)”, incorporated herein by reference, available from http://www.3gpp.org). The MBMS service is a downlink multicast service for transmitting the same downlink data to a plurality of recipients through a radio network. The recipients typically share one radio channel, a shared radio bearer for the reception of MBMS service data. The MBMS service supports the transmission of multimedia data such as real-time image and voice or text. It may therefore also be used to provide data of IMS services to the users. As the same data is transmitted to many users probably located in different cells, the type of connection, PTP or PTM, used in a cell for a specific mobile terminal of the user is based on the number of users located in each cell.
In the following, an exemplary setup procedure for such an IMS service using the MBMS service framework for downlink data provision as described in 3GPP TSG-SA WG2 #48, S2-052305, Sophia Antipolis, France 5-9 Sep. 2005, “Enable IMS service with multicast capability” (incorporated herein by reference, available at http://www.3gpp.org/ftp/tsg_sa/WG2_Arch/TSGS2—48-Sophia_Antipolis/Docs/) is briefly discussed in the following.
First, the user subscribes to an IMS service by sending a INVITE message to the service provider via the radio access network and the core network. After authorizing the user to receive the service, the service provider initiates the reservation of system resources in the mobile communication system, including the setting up of tunnels between a Gateway GPRS support node (GGSN)—Service GPRS support node (SGSN) and a radio network controller (RNC), for controlling radio transmission resources in the RAN. Furthermore, a radio bearer between the RNC and the user equipment (UE) is established for the signalling and the uplink connection from the UE to the service provider. For communicating, session setup signalling, session setup and control protocols as SIP (Session Initiation Protocol) are used.
To provide the downlink data to the users, the MBMS service framework is utilized. The setup procedure of the MBMS service can be initiated for example by the IMS service provider. The MBMS setup also includes the configuration of system resources for the transmission of the downlink IMS data. Accordingly, this setup typically comprises the establishment of tunnels between GGSN, SGSN and RNC, described by contexts established in the respective network nodes and further comprises the setup of a shared or dedicated radio bearer in the RAN, depending on the users located in the cell to receive the IMS service.